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Anaesthetics > Electrical Safety > Flashcards

Electrical Safety Flashcards

1
Q

Danger of electric shock is influenced by?

A

Overall current strength
Type and frequency of a current
Local current density

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2
Q

What is the UK mains supply?

A

Alternating AC current

Frequency of 50Hz

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3
Q

Which is more harmful during electrocution? AC OR DC

A

AC = flow back and forth
DC = one directional current
AC worse for shock

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4
Q

Describe the voltages of electrical power from substation to plug

A

16kV at power stations

240V at substation

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5
Q

What is Ohms law?

A

V = IR for direct current

Current flowing through a resistance is proportional to the potential difference across it.

Alternating current uses the term impedance z instead of R, V=IZ

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6
Q 
Symptoms at different currents of macroshock:
Up to 5mA
10-20mA
50mA
100-300mA
A

Up to 5mA - tingling
10-20mA - pain, sustained muscle contraction (15mA threshold for human to let go of electric fence)
50mA - ventricular ectopics/ arrest/ burns
100-300mA - VF (risk increased if shock occurs during depolarisation of cardiac cells, early T wave)
Macroshock via skin passing between 2 different sites of the body

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7
Q

What is impedance?

A

Variation of resistance to flow of AC in relation to AC frequency
1 ohm = Z
Conductors have low impedence
Insulators have high impedence
ie Dry skin 10k ohms
Impedence falls if surface of skin is wet or high area of contact
High impedence is protective
High frequency moves through skin quickly
Defibrillators and diathermy use principle

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8
Q

What current is generated if a dry hand touches a love wire at mains?

A

V = IZ
240 / 10000 = I
I = 24mA

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9
Q

What does the addition of gel to ECG leads achieve?

A

Lowers impedence to allow electrical signal across chest

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10
Q

Area of entry to exit increases the current density does what?

A

Reduces

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11
Q

How does unipolar diathermy work?

A

A high frequency current is passed through a fine blade or forceps and returns via a large low impedence pad. The current density is high at the tip producing an intense heat.

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12
Q

How does nerve stimulation work?

A

The closer the needle is placed to the nerve the lower the current required to achieve successful motor stimulation. 0.5mA

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13
Q

Faulty device connected to a cardiac device may cause what?

A

Microshocks at potentially very low currents (mA)
A microshock occurs when in direct or close contact with the myocardium
Major cause is a leakage current because of incomplete insulation.
Devices: pacemaker, CVC (saline column a conductor) , ECG

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14
Q

A floating circuit is what?

A

Achieved using a transformer which generates an identical electrical source (using electromagnetic induction) but breaks the continuous circuit between mains supply and patient.
Reduces risk of high current leakage
Draw the symbol

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15
Q

Describe the different leakage circuits?

A

CF - most insulated equipment as usual cardiac connections. Floating circuit. 1 (0.05mA) or 2 (0.01mA)
BF - for equipment with no direct cardiac connections e.g. ECG. Floating circuit
B - class 1 (0.5mA) or 2 (0.1mA), least stringent. It is earthed with no floating circuit.
A is unsafe and not use in medical equipment

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16
Q

How are accidental shocks prevented?

A

Insulation - prevents electrical contact between body and love electrical source, high impedence to minimise the current if aberrant conduction occurs
Cut out mechanism - fuse melts if current surges, circuit breaker (COELCB) cuts supply if imbalance in current (thinks current has found another pathway to earth)

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17
Q

What are the 3 classes of insulation? British standard.

A

Class 1 - any exposed metal must be connected to earth, in combination with cut out mechanism i.e. Fuse
Class 2 - double insulation, no earth connection
Class 3 - battery powered < 40v DC. Isolating transformer if AC 24V (SELV)

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18
Q

Ampere - describe as SI unit

A

Unit of current = flow of charge/sec = 1 Q/second
Constant current which if maintained in 2 straight parallel conductors of infinite length, of negligible circular cross section, and placed 1m apart in a vacuum, would produce between those conductors a force equal to 2x10-7 N per m of length

19
Q

Describe capacitance

A 
Stored electrical charge
2 plates separated by an insulator hold a potential difference
Size and distance 
Switch releases a charge
1 Farad = capacitance 
1 coulomb 1m^2 plate 1m apart
20
Q

Inductance means

A

Induction of an electrical field Ina wire moving in a magnetic field
Dynamo

21
Q

What is the unit of power

A

Watt = energy used/ unit of time = I^2R

22
Q

What is the unit of electric potential?

A

1 Volt = 1W for the flow of 1 Amp

V = W/I

23
Q

What is electrical charge?

A

A charged body can either be positive or negative.
Electrons negative. Nucleus positive.
1 coulomb is the quantity of electrical charge that passes a point when the current of 1 amp flows for a period of 1 second
1 coulomb = unit of charge (Q) = number of electrons = 6.241x10^18 electrons (mol)

24
Q

What is a joule?

A

Unit of energy

25
Q

Draw AC vs DC graph

Draw diagram

A

See picture

Volts over time

26
Q

Draw a defibrillator circuit

A

See picture

27
Q

Risks of electricity

A 
Burns
Fires 
Explosions
Cardiac arrythmias
Death
28
Q

Static risk increases in what climate?

A

Humidified 50% 20C

29
Q

How does electricity flow through the body?

A

Resistive coupling - passes through body from source of faulty equipment to earth (bed metal)
Capacitative coupling - body acts on side of capacitor with an electrical device (lights/MRI). Burns can occur

30
Q

How do you protect a patient and yourself from electricity?

A

Ensure no contact with devices and earthed objects or floor
Wear rubber antistatic shoes
Avoid diathermy in patients with metal implants
Think about earth/ equipotential earth/ current leakage/ insulation
Rubber gloves
Prevent humidity
Floating circuits

31
Q

How does bipolar diathermy differ from unipolar?

A

Lower power
Forceps
Very small distance for current to travel

32
Q

Temperature is what?

A

A measure of energy state

Kinetic

33
Q

How is temperature measured?

A 
Non electronic
Mercury
Alcohol
Bimetallic strips
Bourdon gauge (party whistle like)

Electronic
Platinum resistance wire
Thermistor
IR radiation

34
Q

What is the Seebeck effect?

A

2 dissimilar metals in close proximity will develop a potential difference between them.
The PD is temperature dependent
Draw diagram

35
Q

What is a transducer?

A

An energy form changer
I.e. US is electrical to kinetic to sound
Change in resistance changes current

NB An art line transducer does not convert the pulse into energy. A wire moves with the pulse creating kinetic energy

36
Q

Draw platinum resistance graph and describe mechanism of action

A

See graph

37
Q

What is a thermistor?

Draw the graph

A

A bead of semiconducting metal oxide

Ohms v temperature

38
Q

What is the weight stone bridge equations and diagram?

A

R1/R2 = R3/R4

R1/R2 are known values
R3 is a variable
R4 measurement

39
Q

What is electric current?

A

Rate of passage of electrons through a substance i.e. rate of passage of an electric charge
1 ampere = 1 coulomb per second
DC and AC

40
Q

DC is found in what?

A

Batteries and thermocouples

41
Q

What is resistance?

A

This is the opposition to a flow of a DC along a conductor. Not frequency dependent. Measured in ohms.

42
Q

What are the sources of interference in biological signals?

A

ECG upset
External
Capacitative coupling in AC current (both patient and AC current are connected to earth)
Could place earthed screen between or move patient further away plus insulator)
Remove with differential operational amplifier!
Internal
Shivering
Movement
Place electrodes over boney prominences.

43
Q

Main supply preventative measures to reduce electrocution involve?

A

Isolation transformers
Earth leakage breakage circuit
Residual current devices
Leakage current monitors

Anaesthetics (12 decks)

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